Means for preventing electrical interfer ence



R. B. SHANCK MEANS FOR PREVENTING ELECTRICAL INTERFERENCE June 28, 1927.

Filed May 6, 1922 w W M 1. w

"FF/TOR. A. 15. Jlma ATTORNEY Patented June 28, 1927.

U ITED STATES 1,633,611 PATENT OFFICE.

ROY B. SHANCK, OF WOODSIDE, NEW YORK, ASSIGNOR TO AMERICANTELEPHONE AND TELEGRAPH COMPANY,

A CORPORATION OF NEW YORK.

MEANS FOR PREVENTING ELECTRICAL INTERFERENCE.

Application filed May 6, 1922. Serial No. 559,029.

This invention relates to means for preventing electrical interferen e and especially to an arrangement for preventing that form of interference between single-line grounded telegraph circuits, which is termed cross-fire.

1n the operation of grounded telegraph circuits it is well known that when signaling impulses are transmitted over one telegraph circuit, an interfering current will be set up in other circuits paralleling the first circuit, due to the mutual admittance between the circuit over which the impulses are being transmitted, hereinafter referred to as the disturbing circuit. and the circuit or circuits paralleling the said first circuit, hereinafter referred to as the disturbed circuit or circuits. This interfering current will cause a disturbance in the terminal apparatus at both ends of the disturbed circuit. The disturlr ance set up in the terminal apparatus of a disturbed circuit located in the same station in which is also located the terminal apparatus from which the signaling impulses are being impressed upon the said disturbing circuit. may be termed sending-end crossfire. The disturbance set up in the terminal apparatus of the disturbed circuit located in the same station in which is also located the receiving apparatus of the said disturbing circuit, may be termed receiving-end crossfire.

Various methods and means for neutralizing both types of cross-tire in duplex or half-duplex telegraph circuits have been described in the copending application of Shanck, Serial No. 473,118, filed May 27, 1921. and that of Cory, Serial No. 533,370, filed February 1, 1922.

It is the object of the present invention to prevent or to minimize telegraph cross-fire in single-line Morse circuits, which as will be shown, are structurally and operatively different from the duplex and half-duplex circuits heietofore referred to.

This invention will be better from the following description when read in connection with the attached drawing, of which Figure 1 shows a form of embodiment of the invention using a capacitive coupling; Fig. 2 shows a form using an inductive coupling, and Fig. 3 shows the application of the form of the invention shown in Fig. 2 to a network involving more than two line circuits.

understood In Fig. 1, 1 and 2 represent two line ciruits, the former of which will be considered. for the purpose of describing this invention, as the disturbing circuit, and the latter the disturbed circuit, that is to say. the transmission of signaling impulses over line 1 will set up an interfering or crossfire current in line 2 by virtue of. the mutual ad mittance represented in the drawing by condensers connected by dotted conductors between the two lines. The line 1 has connected therewith at the station A a key 3, a source of direct current 4 and a main line relay 5. In similar manner there is connected with the line 1 at station B a key 6, a source of direct current 7, the polarity of which is opposite that of the source 4, and a main line relay 8. At station A there is also connected into the line 1 the winding of a relay 15. forming part of the cross-fire neutralization equipment which will presently be described in full.

The line circuit 2 has connected therewith at station A a key 9, a source of direct current 10 and a main line relay 11, and similarly at station B, a key 12, a source of direct current 13, the polarity of which is opposite that of the source 10, and a main line relay line circuit 2 is connected preferably at station A with the armature 16 of the neutralizing relay, the said connection including in series a condenser 19 and a resis ance 20. The armature 16 is adapted to 11101 6 between two contacts, the left-hand one of which is connected with a source of direct current 17 of opposite polarity to source 4 and the right-hand one is connected to ground through an impedance 18.

Having in mind the foregoing description of the circuit in which this invention cmbodied it will be clearly understood from the following description of the mode of operation of the circuit.

Assume that the line 2 is not being operated, which means that the keys 9 and 12 are closed. Also assume that signals are being sent from station A to station B, in which event the key 6 at B will be kept closed and the key 3 at A will be opened and closed, depending upon the type of signal to be transmitted. lvhen key 3 is closed an impulse of current will flow from station A to station B in the direction represented by the solid arrows. The transmission of such an impulse over the line 1 will set up in the disturbed circuit 2 a cross-tire current represented by the wavy arrows. This current Will flow in opposite d rections in the said circuit 2, depending upon the magnitude 0 f the impedance to ground in the two directions. lVhen the signal impulse was transmitted over the line i by the closing of the key 3, the relay 1?; was operated. Which connected the negative battery 1''? to the line circuit 2 through the condenser it; and resistance 20. here would accord ng ly occur in the line circu t 2 a transitory flow of current in the directions r presented by the dotted arrows. the duration of which would depend upon the capacity of the c01ldenser l9 and the value of resistance ill. By the proper adjustment of the constants of the neutralizing circuit the magnitudes of the crossfire current, and the neutralizing current, may be made substantiallyequal, thereby effecting proper neutralization of the disturbing currents.

\Vhen the key 3 is open for the tltll'lrmission of a space signal to the distant station, current will cease to now in th line 1 and consequently the reiay i5, is deenergized, thereby connecting the line circuit 2 to ground, the connection including resistance 20, condenser 19 and the impedance 18. Since the battery & is disconnected from line 1, the said line assumes a negative potential with respect to the earth, due to the connection therewith of th source 7. This occasions a cross-lire current in the line 2 which will be opposite to that shown by the wavy arrows in Fig. l. Therefore, in order to neutralize this cross-lire current the direction of the neutralizing current must be opposite. Thus, when the armature ltl moves to the right and touches the contact that connects the impedance 1%. in series therewith, some of the energy of the con-- denser 19 Will be given up, causing a current to flow in the, direction opposite to that represented by the dotted arrows in the figure.

Fig. 2 shows the application of the principle of this invention to a single line Morse circuit by means of an inductive coupling. The same reference numerals used in Fig. 1 have been used in this figure to reprrseni similar parts. Connected in the circuit oi the line 1 is the primary winding ll of a transformer 30, the secondary winding of which, 32, is connected between ground and the line circuit 2. the connection including a resistance and a condenser Sill'lllarly, there has been connected in series with the line circuit 2 a primary winding l t of l transformer h), the secondary of which, 4;. has been connected between ground and the line circuit 1, the connection including a resistance 43 and condenser 44-. Similar transformers Q0 and 60 have been connected in a similar manner with the circuits 1 and 2 at the d stant station B.

When the keys of the line circuit 3 rc closed, as shown in the figure, and key 3 of line circuit 1 is dosed in order to transmit a marking impulse to the distant station B, current tlows through the primary winding 31 of the transformer 30, which induces in the secondary 25; a potential such as to cause current to flow in the said secondary winding in opposite direction to the current in the line circuit This current in the secondary winding represented by the dotted arrow. it will accordingly be seen that the interfering cross-lire current set. up in the line 2 (represented by the war y arrow) will be oppos :1 in direction y the neutralir iing current represented by the dotted arrows. The magnitude of the neutralizing current may be controlled by the proper adjustment of the constants of the neutralizing circuit so as to substantially equal the int-crlering current and therefore to prevent any effect of the latter upon the relays at either end of the exposed circuit 2,

\Vhen the key 13 is opened for the transmission of a space signal the direction of the interfering current in the line 2 will he opposite that shown in the figure. The change of current in line it induces a current which will flow in the exposed circuit 2 in a direction opposite to that. represented by the dotted arrows of the ligurc, so that the interfering current will be new tralized. The tansformers 5t and (El), repre ented at the distant station ll, function in the same manner the transformers 11) and ltl, shown at station 1 and it is believed that further description of them is not necessary.

Fig. 3 shows the application of this inrcntion, in the form shown in Fig. 2, to three line circuits. in this figure are shown three transformers, 130, 4 t) and TO. the priniaries of which, 31, ll and Ti, are conncctrd in series with the line circuits 1, 2 and 3. The secondary 35 and the secondary 4 5 are connected in series between ground and the line circuit 1). the said connection including a condenser b. Similarly, the secondary 32 and the serondury T2 are connected in seri s bet ween the ground and the line circuit 2, the said con nefH-az including the condenser C and in lllit, manner the secondary 9.2 and the ec ondary are connected in series between the ground and the line circuit 1, the said connection including the condenser 0,. iv this inductive intercomnx*tion of the various lines i'ha make up the network it will be seen that. a neutralizing impulr'e is t-icl' up in e iry other line circuit of the network when a signaling impulse is transmitted over one of the lines of the said uetworla.

in the case of a large gauge cable circuits,

receiving-end cross-tire is ordinarily larger than the sending cud cross-tire, making neutralization somewhat ditlicult by the methods heretofore described. It is believed however, that by allowing the sending-cud crosslire to be o.'er-neutralizid when the exposed circuit is closed. sutiicient neutralization of the receivingcnd cross ire caa be secured. hen the. key of the exposed circuit is open, the impulse tor neutralizing receiving-end cross-tire is considerably greater, but probably will not be great enough to cause serious over-neutralization.

It will be seen that by the means of this invention, several forms of which are shown and described herein, crossfire interference between a plurality of single-line Morse cir cuits may be substaiitiall neutralized or prevented. From the foregoing description it will be noted that the problem of neutralizing cross tire bet ween single-line lilorse circuit is ditlcreot from that of neutralizing cross t'ire between duplex or halfduplex circuits, inasmuch as in the first mentioned circuit, the impedance of the disturbed line circuit varies for ditl'erent positions of its sending lrcy at the 7 home station. whereas in the duplex or halt-cuplex circuit, the position of the key on the disturbed circuit has no bearing upon the impedance of the exposed circuit. Furthermore. owing to the fact that single-line Morse circuits ha\e no neutral point such as it provided by the balanced ratio arms in duplex or half-duplex circuits, it is impracticable in the former type of circuit to neutralize independently the sending-end and receiving-cml cross-tire, which can be done in the case of the duplex or half-duplex circuit. as fully described in the said copending applications heretofore referred to.

Although this invention has been disparticular forms forms but: is capvariety of forms appended claims.

closed as embodied in it is not limited to these able of embodiment in a. within the scope of the What is claimed is:

1. In a single-line Morse telegraph system. the method for substantially neutralizing crossfire which consists in impressing a signaling impulse upon one of the circuits of the said system, causing the said impuls to create a neutral zing impulse in each of the other circuits of the said system in such directions as to prevent both the receivingcnd and the sending-end cross-tire impulses.

2. In a single-line Morse telegraph system, the method for substantially neutralizing crossfire. which consists in impressing a signaling impulse upon one of the circuits of the said system. causing the said impulse to create a difference of potential to ground in the other circuits of the said systen'i, whereby all of the cross-tire currents produced by the mutual admittance between the circuits of the said system may be neutralmed.

3. In a single-line Morse telegraph systcm, the method for minimizing cross-tire. which consists in lIl'lPl'QSSlDg a signal impulse upon one or the circuits of the said system, thereby producing interfering inipulses in another circuit of the said system, and controlling the production of neutralizing impulses in the said other circuit, the direction of propagation of the said neutralizing impulses being such as to oppose and neutralize the interfering impulses throughout the said other circuit.

et. in a single-line Morse telegraph System, the combination with two single-line Morse circuits, of a transformer, one Winding of which is connected in series with one of said Morse circuits, and the other winding of which is connected in series with a condenser between the other of said Morse circuits and ground.

5. In a single-line Morse telegraph sys tem, the combination with two single-line Morse circuits, of a transforn'ier, one wind ing of which is connected in series with one of aid Morse circuits, and the other winding of which is connected in series with a condenser and a resistance between the other of said ii'lorse circuits and ground.

6. In a single-line. Morse telegraph system. the combii'iation with two single-line Morse circuits, of a plurality of transformers, each of which has one of its windings in series with one of the said Morse circuits, and the other in series winding connected with a condenser between said other Morse circuit and ground.

7. In a single-line Morse telegraph system, the combination with two single-line Morse circuits, of a plurality of transformers, each of which has one of its windings in series with one of the said Morse circuits. and the other winding connected in series with a condenser and a resistance between said other Morse circuits and ground.

8. In a. single-line Morse telegraph System, the combination with a plurality of single-line Morse circuits, of a plurality of multiwinding transformers, each of which has one wint'ling connected in series with one of said Morse circuits, and each of the other windings connected in series with a condenser between one of the other Morse circuits and ground.

9. In a single-line Morse telegraph system, the combination with a plurality of single-line Morse circuits, of a. plurality of multiwinding transformers, individual to and each having one winding connected in series with one of said Morse circuits, and each line hav ng connected to it a path to ground containing a condenser, a resistance and another winding of each of the said transformers associated with the other lines.

10. In a single-line Morse telegraph system. the combination with a plurality of single-line Morse circuits, of a, plurality of multiwinding' transformers individual to and each having one winding connected in series with one of said Morse circuits, and the other windings of the respective transformers arranged in groups. each group being connected in enes; with a condenser be- 10 tween :1 line circuit and ground.

1n testimony whereof, I have signed my name to this pecification this 5th day of May, 1922.

ROY B. SHANCK. 

